The importance of proteoglycans in articular cartilage

The human body experiences a wide variety of stresses from loading produced by its own weight or external forces such as gravity. To prevent any damage to the bones, especially during movement, nature has designed special cushioning that is called hyaline cartilage. Hyaline is primarily found at the tips of long bones that make up our limbs, also referred to as articular cartilage. The major function of articular cartilage is to absorb shock and to lubricate the bones during movement. This specific function of hyaline is underlied by its composition. A major player in hyaline cartilage are large molecules that are called proteoglycans: ‘proteo’ meaning protein and ‘glyco’ meaning sugar. These molecules can attract and retain water inside the cartilage which gives it its shock-absorbing properties. In addition to the proteoglycans, there is a network of strands that can be aligned or randomly dispersed within the cartilage. This network provides structure and stiffness to the hyaline, and together with the proteoglycans determine cartilage functions. In this mini-review the major types of proteoglycans and their roles in hyaline were summarised. Moreover, hyaline proteoglycans were compared to proteoglycans in other types of cartilage such as mature or diseased cartilage.